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14/10/2015
1
Giorgio ButtazzoE-mail: [email protected]
Scuola Superiore Sant’Anna
Definition
Real-Time Systems are computing systems that must perform computation within given timing constraints.
They are typically embeddedin a larger system to control its functions:
Real-Time Embedded Systems
EmbeddedComputer
Controlled System
Sensors
Motors
Evolution of Embedded Systems
Embedded computing systems have grownexponentially in several application domains:
1970 1990 2000 20100
Number ofembeddedcomputers
1980 year
avionics
robotics
automotive
consumer electronics
multimedia
Computers everywhere
Today, 98% of all processors in the planet areembedded in other objects:
Typical applications
avionics
automotive
robotics
industrial automation
telecommunications
multimedia systems
consumer electronics
From Hardware to Software
We are experiencing a dematerialization process inwhich many functions are converted into software.
Examples– Money
– Documents– Books
– Music
– Pictures– Movies
– Tickets
– Education
14/10/2015
1
Giorgio ButtazzoE-mail: [email protected]
Scuola Superiore Sant’Anna
Definition
Real-Time Systems are computing systems that must perform computation within given timing constraints.
They are typically embeddedin a larger system to control its functions:
Real-Time Embedded Systems
EmbeddedComputer
Controlled System
Sensors
Motors
Evolution of Embedded Systems
Embedded computing systems have grownexponentially in several application domains:
1970 1990 2000 20100
Number ofembeddedcomputers
1980 year
avionics
robotics
automotive
consumer electronics
multimedia
Computers everywhere
Today, 98% of all processors in the planet areembedded in other objects:
Typical applications
avionics
automotive
robotics
industrial automation
telecommunications
multimedia systems
consumer electronics
From Hardware to Software
We are experiencing a dematerialization process inwhich many functions are converted into software.
Examples– Money
– Documents– Books
– Music
– Pictures– Movies
– Tickets
– Education
14/10/2015
1
Giorgio ButtazzoE-mail: [email protected]
Scuola Superiore Sant’Anna
Definition
Real-Time Systems are computing systems that must perform computation within given timing constraints.
They are typically embeddedin a larger system to control its functions:
Real-Time Embedded Systems
EmbeddedComputer
Controlled System
Sensors
Motors
Evolution of Embedded Systems
Embedded computing systems have grownexponentially in several application domains:
1970 1990 2000 20100
Number ofembeddedcomputers
1980 year
avionics
robotics
automotive
consumer electronics
multimedia
Computers everywhere
Today, 98% of all processors in the planet areembedded in other objects:
Typical applications
avionics
automotive
robotics
industrial automation
telecommunications
multimedia systems
consumer electronics
From Hardware to Software
We are experiencing a dematerialization process inwhich many functions are converted into software.
Examples– Money
– Documents– Books
– Music
– Pictures– Movies
– Tickets
– Education
14/10/2015
1
Giorgio ButtazzoE-mail: [email protected]
Scuola Superiore Sant’Anna
Definition
Real-Time Systems are computing systems that must perform computation within given timing constraints.
They are typically embeddedin a larger system to control its functions:
Real-Time Embedded Systems
EmbeddedComputer
Controlled System
Sensors
Motors
Evolution of Embedded Systems
Embedded computing systems have grownexponentially in several application domains:
1970 1990 2000 20100
Number ofembeddedcomputers
1980 year
avionics
robotics
automotive
consumer electronics
multimedia
Computers everywhere
Today, 98% of all processors in the planet areembedded in other objects:
Typical applications
avionics
automotive
robotics
industrial automation
telecommunications
multimedia systems
consumer electronics
From Hardware to Software
We are experiencing a dematerialization process inwhich many functions are converted into software.
Examples– Money
– Documents– Books
– Music
– Pictures– Movies
– Tickets
– Education
14/10/2015
1
Giorgio ButtazzoE-mail: [email protected]
Scuola Superiore Sant’Anna
Definition
Real-Time Systems are computing systems that must perform computation within given timing constraints.
They are typically embeddedin a larger system to control its functions:
Real-Time Embedded Systems
EmbeddedComputer
Controlled System
Sensors
Motors
Evolution of Embedded Systems
Embedded computing systems have grownexponentially in several application domains:
1970 1990 2000 20100
Number ofembeddedcomputers
1980 year
avionics
robotics
automotive
consumer electronics
multimedia
Computers everywhere
Today, 98% of all processors in the planet areembedded in other objects:
Typical applications
avionics
automotive
robotics
industrial automation
telecommunications
multimedia systems
consumer electronics
From Hardware to Software
We are experiencing a dematerialization process inwhich many functions are converted into software.
Examples– Money
– Documents– Books
– Music
– Pictures– Movies
– Tickets
– Education
14/10/2015
1
Giorgio ButtazzoE-mail: [email protected]
Scuola Superiore Sant’Anna
Definition
Real-Time Systems are computing systems that must perform computation within given timing constraints.
They are typically embeddedin a larger system to control its functions:
Real-Time Embedded Systems
EmbeddedComputer
Controlled System
Sensors
Motors
Evolution of Embedded Systems
Embedded computing systems have grownexponentially in several application domains:
1970 1990 2000 20100
Number ofembeddedcomputers
1980 year
avionics
robotics
automotive
consumer electronics
multimedia
Computers everywhere
Today, 98% of all processors in the planet areembedded in other objects:
Typical applications
avionics
automotive
robotics
industrial automation
telecommunications
multimedia systems
consumer electronics
From Hardware to Software
We are experiencing a dematerialization process inwhich many functions are converted into software.
Examples– Money
– Documents– Books
– Music
– Pictures– Movies
– Tickets
– Education
14/10/2015
2
Sensor
MotorSensorMotor
ControlUnit
Steer by Wire Why?
1. Software is more flexible than hardware
2. It can be quickly changed/adapted/updated
3. It can be upgraded remotely
4. It can evolve into intelligent control algorithms
5. It has no mass, so it can travel at the speed of light
There are many advantages
Increasing complexity
Related problems
Difficult design
Less predictability
Less reliability
The price to be paid is a higher software complexity .
Novel solutions for:
Component-based software design
Analysis for guaranteeing predictability and safety
Testing
Complexity and bugs
Software bugs increase with complexity:
1 K 100 K 1 M 10 M0
10
100
1000
10.000
10K
Lines of code
bugs
Reliability does not only depend on the correctness ofsingle instructions, but also on when they areexecuted:
controller
output
inputt
t +
A correct action executed too late can be useless oreven dangerous.
Software reliability Real-Time Systems
Computing systems that must guaranteebounded and predictable response timesare called real-time systems .
Predictability of response times must be guaranteed
for each critical activity;
for all possible combination of events.
14/10/2015
2
Sensor
MotorSensorMotor
ControlUnit
Steer by Wire Why?
1. Software is more flexible than hardware
2. It can be quickly changed/adapted/updated
3. It can be upgraded remotely
4. It can evolve into intelligent control algorithms
5. It has no mass, so it can travel at the speed of light
There are many advantages
Increasing complexity
Related problems
Difficult design
Less predictability
Less reliability
The price to be paid is a higher software complexity .
Novel solutions for:
Component-based software design
Analysis for guaranteeing predictability and safety
Testing
Complexity and bugs
Software bugs increase with complexity:
1 K 100 K 1 M 10 M0
10
100
1000
10.000
10K
Lines of code
bugs
Reliability does not only depend on the correctness ofsingle instructions, but also on when they areexecuted:
controller
output
inputt
t +
A correct action executed too late can be useless oreven dangerous.
Software reliability Real-Time Systems
Computing systems that must guaranteebounded and predictable response timesare called real-time systems .
Predictability of response times must be guaranteed
for each critical activity;
for all possible combination of events.
14/10/2015
2
Sensor
MotorSensorMotor
ControlUnit
Steer by Wire Why?
1. Software is more flexible than hardware
2. It can be quickly changed/adapted/updated
3. It can be upgraded remotely
4. It can evolve into intelligent control algorithms
5. It has no mass, so it can travel at the speed of light
There are many advantages
Increasing complexity
Related problems
Difficult design
Less predictability
Less reliability
The price to be paid is a higher software complexity .
Novel solutions for:
Component-based software design
Analysis for guaranteeing predictability and safety
Testing
Complexity and bugs
Software bugs increase with complexity:
1 K 100 K 1 M 10 M0
10
100
1000
10.000
10K
Lines of code
bugs
Reliability does not only depend on the correctness ofsingle instructions, but also on when they areexecuted:
controller
output
inputt
t +
A correct action executed too late can be useless oreven dangerous.
Software reliability Real-Time Systems
Computing systems that must guaranteebounded and predictable response timesare called real-time systems .
Predictability of response times must be guaranteed
for each critical activity;
for all possible combination of events.
14/10/2015
2
Sensor
MotorSensorMotor
ControlUnit
Steer by Wire Why?
1. Software is more flexible than hardware
2. It can be quickly changed/adapted/updated
3. It can be upgraded remotely
4. It can evolve into intelligent control algorithms
5. It has no mass, so it can travel at the speed of light
There are many advantages
Increasing complexity
Related problems
Difficult design
Less predictability
Less reliability
The price to be paid is a higher software complexity .
Novel solutions for:
Component-based software design
Analysis for guaranteeing predictability and safety
Testing
Complexity and bugs
Software bugs increase with complexity:
1 K 100 K 1 M 10 M0
10
100
1000
10.000
10K
Lines of code
bugs
Reliability does not only depend on the correctness ofsingle instructions, but also on when they areexecuted:
controller
output
inputt
t +
A correct action executed too late can be useless oreven dangerous.
Software reliability Real-Time Systems
Computing systems that must guaranteebounded and predictable response timesare called real-time systems .
Predictability of response times must be guaranteed
for each critical activity;
for all possible combination of events.
14/10/2015
3
efficiency predictability
Predictability vs. Efficiency
Allocated resources
QoS management High performance Safety critical
digital tvsoft firm hard
Criticality
What’s special in Embedded Systems?
FEATURES
Scarce resources (space, weight, time, memory, energy)
High concurrency and resource sharing (high task interference)
Interaction with the environment
(causing timing constraints)
High variability on workload and resource demand
REQUIREMENTS
High efficiency in resource management
Temporal isolation to limit the interference
High predictability in the response time
Adaptivity to handle overload situations
Aim of the Course
Studying software methodologies for supportingtime critical computing systems.
We will not consider how to control a system,but only how to provide a predictable softwaresupport to control applications.
Main focus: predictable software
Design
Analysis
Programming
Sensoryprocessing
Control
Commun.
software
Graphics
EmbeddedComputer
Controlled System
systemdynamics
Control and implementation
Often, control and implementation are done bydifferent people that do not talk to each other:
Control guys typically assume a computer with infiniteresources and computational power. In some case,computation is modeled by a fixed delay .
In reality, a computer:
has limited resources;
finite computational power (non null execution times);
executes several concurrent activities;
introduces variabile delays (often unpredictable).
Modeling such factors and taking them into accountin the design phase allows a significantimprovement in performance and reliability.
Control and implementation
14/10/2015
3
efficiency predictability
Predictability vs. Efficiency
Allocated resources
QoS management High performance Safety critical
digital tvsoft firm hard
Criticality
What’s special in Embedded Systems?
FEATURES
Scarce resources (space, weight, time, memory, energy)
High concurrency and resource sharing (high task interference)
Interaction with the environment
(causing timing constraints)
High variability on workload and resource demand
REQUIREMENTS
High efficiency in resource management
Temporal isolation to limit the interference
High predictability in the response time
Adaptivity to handle overload situations
Aim of the Course
Studying software methodologies for supportingtime critical computing systems.
We will not consider how to control a system,but only how to provide a predictable softwaresupport to control applications.
Main focus: predictable software
Design
Analysis
Programming
Sensoryprocessing
Control
Commun.
software
Graphics
EmbeddedComputer
Controlled System
systemdynamics
Control and implementation
Often, control and implementation are done bydifferent people that do not talk to each other:
Control guys typically assume a computer with infiniteresources and computational power. In some case,computation is modeled by a fixed delay .
In reality, a computer:
has limited resources;
finite computational power (non null execution times);
executes several concurrent activities;
introduces variabile delays (often unpredictable).
Modeling such factors and taking them into accountin the design phase allows a significantimprovement in performance and reliability.
Control and implementation
14/10/2015
3
efficiency predictability
Predictability vs. Efficiency
Allocated resources
QoS management High performance Safety critical
digital tvsoft firm hard
Criticality
What’s special in Embedded Systems?
FEATURES
Scarce resources (space, weight, time, memory, energy)
High concurrency and resource sharing (high task interference)
Interaction with the environment
(causing timing constraints)
High variability on workload and resource demand
REQUIREMENTS
High efficiency in resource management
Temporal isolation to limit the interference
High predictability in the response time
Adaptivity to handle overload situations
Aim of the Course
Studying software methodologies for supportingtime critical computing systems.
We will not consider how to control a system,but only how to provide a predictable softwaresupport to control applications.
Main focus: predictable software
Design
Analysis
Programming
Sensoryprocessing
Control
Commun.
software
Graphics
EmbeddedComputer
Controlled System
systemdynamics
Control and implementation
Often, control and implementation are done bydifferent people that do not talk to each other:
Control guys typically assume a computer with infiniteresources and computational power. In some case,computation is modeled by a fixed delay .
In reality, a computer:
has limited resources;
finite computational power (non null execution times);
executes several concurrent activities;
introduces variabile delays (often unpredictable).
Modeling such factors and taking them into accountin the design phase allows a significantimprovement in performance and reliability.
Control and implementation
14/10/2015
3
efficiency predictability
Predictability vs. Efficiency
Allocated resources
QoS management High performance Safety critical
digital tvsoft firm hard
Criticality
What’s special in Embedded Systems?
FEATURES
Scarce resources (space, weight, time, memory, energy)
High concurrency and resource sharing (high task interference)
Interaction with the environment
(causing timing constraints)
High variability on workload and resource demand
REQUIREMENTS
High efficiency in resource management
Temporal isolation to limit the interference
High predictability in the response time
Adaptivity to handle overload situations
Aim of the Course
Studying software methodologies for supportingtime critical computing systems.
We will not consider how to control a system,but only how to provide a predictable softwaresupport to control applications.
Main focus: predictable software
Design
Analysis
Programming
Sensoryprocessing
Control
Commun.
software
Graphics
EmbeddedComputer
Controlled System
systemdynamics
Control and implementation
Often, control and implementation are done bydifferent people that do not talk to each other:
Control guys typically assume a computer with infiniteresources and computational power. In some case,computation is modeled by a fixed delay .
In reality, a computer:
has limited resources;
finite computational power (non null execution times);
executes several concurrent activities;
introduces variabile delays (often unpredictable).
Modeling such factors and taking them into accountin the design phase allows a significantimprovement in performance and reliability.
Control and implementation
14/10/2015
3
efficiency predictability
Predictability vs. Efficiency
Allocated resources
QoS management High performance Safety critical
digital tvsoft firm hard
Criticality
What’s special in Embedded Systems?
FEATURES
Scarce resources (space, weight,
time, memory, energy)
High concurrency and resource
sharing (high task interference)
Interaction with the environment
(causing timing constraints)
High variability on workload and
resource demand
REQUIREMENTS
High efficiency in resource
management
Temporal isolation to limit
the interference
High predictability in the
response time
Adaptivity to handle
overload situations
Aim of the Course
Studying software methodologies for supportingtime critical computing systems.
We will not consider how to control a system,but only how to provide a predictable softwaresupport to control applications.
Main focus: predictable software
Design
Analysis
Programming
Sensoryprocessing
Control
Commun.
software
Graphics
EmbeddedComputer
Controlled System
systemdynamics
Control and implementation
Often, control and implementation are done bydifferent people that do not talk to each other:
Control guys typically assume a computer with infiniteresources and computational power. In some case,computation is modeled by a fixed delay .
In reality, a computer:
has limited resources;
finite computational power (non null execution times);
executes several concurrent activities;
introduces variable delays (often unpredictable).
Modeling such factors and taking them into accountin the design phase allows a significantimprovement in performance and reliability.
Control and implementation
14/10/2015
4
Specific objectives
Study software methodologies and algorithmsto increase predictability in computing systems.
We consider embeddded computing systemsconsisting of several concurrent activities subjectto timing constratints.
We will see how to model and analyze a real-timeapplication to predict worst-case response timesand verify its feasibility under a set of constraints.
Course outline - 1
1. Basic concepts and terminology
2. Sample applications
3. Problem identification
4. Modeling real-time activities
5. Deriving timing constraints
6. Worst-case reasoning
7. Managing periodic tasks
8. Scheduling algorithms
9. Schedulability analysis
10. Problems introduced by resource sharing
11. Resource access protocols
12. Estimating worst-case blocking times
13. Handling asynchronous (aperiodic) tasks
14. Handling execution overruns
15. Managing overload conditions
16. Real-time communication mechanisms
Course outline - 2
Programming real-time applications Processes and threads in Linux
Thread creation and activation
Linux schedulers
Time management
How implement periodic threads
How to structure RT applications
How to use a graphics library
How to simulate RT control systems
Course outline - 3
23
Teaching material
http://retis.sssup.it/~giorgio/rts-MECS.htmlCourse homepage
Books:
Third EditionPitagora, 2006Third EditionPitagora, 2006
Third EditionSpringer, 2011Third EditionSpringer, 2011
24
Final Exam
It consists of two parts:
1. Project work
2. Written test
Project: Developing a RT application under Linux, usingthe Pthread library and the Allegro graphics library.
Test: A number of questions and exercises on thecourse program.
14/10/2015
4
Specific objectives
Study software methodologies and algorithmsto increase predictability in computing systems.
We consider embeddded computing systemsconsisting of several concurrent activities subjectto timing constratints.
We will see how to model and analyze a real-timeapplication to predict worst-case response timesand verify its feasibility under a set of constraints.
Course outline - 1
1. Basic concepts and terminology
2. Sample applications
3. Problem identification
4. Modeling real-time activities
5. Deriving timing constraints
6. Worst-case reasoning
7. Managing periodic tasks
8. Scheduling algorithms
9. Schedulability analysis
10. Problems introduced by resource sharing
11. Resource access protocols
12. Estimating worst-case blocking times
13. Handling asynchronous (aperiodic) tasks
14. Handling execution overruns
15. Managing overload conditions
16. Real-time communication mechanisms
Course outline - 2
Programming real-time applications Processes and threads in Linux
Thread creation and activation
Linux schedulers
Time management
How implement periodic threads
How to structure RT applications
How to use a graphics library
How to simulate RT control systems
Course outline - 3
23
Teaching material
http://retis.sssup.it/~giorgio/rts-MECS.htmlCourse homepage
Books:
Third EditionPitagora, 2006Third EditionPitagora, 2006
Third EditionSpringer, 2011Third EditionSpringer, 2011
24
Final Exam
It consists of two parts:
1. Project work
2. Written test
Project: Developing a RT application under Linux, usingthe Pthread library and the Allegro graphics library.
Test: A number of questions and exercises on thecourse program.
14/10/2015
4
Specific objectives
Study software methodologies and algorithmsto increase predictability in computing systems.
We consider embeddded computing systemsconsisting of several concurrent activities subjectto timing constratints.
We will see how to model and analyze a real-timeapplication to predict worst-case response timesand verify its feasibility under a set of constraints.
Course outline - 1
1. Basic concepts and terminology
2. Sample applications
3. Problem identification
4. Modeling real-time activities
5. Deriving timing constraints
6. Worst-case reasoning
7. Managing periodic tasks
8. Scheduling algorithms
9. Schedulability analysis
10. Problems introduced by resource sharing
11. Resource access protocols
12. Estimating worst-case blocking times
13. Handling asynchronous (aperiodic) tasks
14. (Handling execution overruns
15. Managing overload conditions
16. Real-time communication mechanisms)
Course outline - 2
Programming real-time applications Processes and threads in Linux
Thread creation and activation
Linux schedulers
Time management
How implement periodic threads
How to structure RT applications
How to use a graphics library
How to simulate RT control systems
Course outline - 3
23
Teaching material
http://retis.sssup.it/~giorgio/rts-MECS.htmlCourse homepage
Books:
Third Edition
Pitagora, 2006
Third Edition
Pitagora, 2006
Third Edition
Springer, 2011
Third Edition
Springer, 201124
Final Exam
It consists of two parts:
1. Project work
2. Written test
Project: Developing a RT application under Linux, usingthe Pthread library and the Allegro graphics library.
Test: A number of questions and exercises on thecourse program.
14/10/2015
4
Specific objectives
Study software methodologies and algorithmsto increase predictability in computing systems.
We consider embeddded computing systemsconsisting of several concurrent activities subjectto timing constratints.
We will see how to model and analyze a real-timeapplication to predict worst-case response timesand verify its feasibility under a set of constraints.
Course outline - 1
1. Basic concepts and terminology
2. Sample applications
3. Problem identification
4. Modeling real-time activities
5. Deriving timing constraints
6. Worst-case reasoning
7. Managing periodic tasks
8. Scheduling algorithms
9. Schedulability analysis
10. Problems introduced by resource sharing
11. Resource access protocols
12. Estimating worst-case blocking times
13. Handling asynchronous (aperiodic) tasks
14. Handling execution overruns
15. Managing overload conditions
16. Real-time communication mechanisms
Course outline - 2
Programming real-time applications Processes and threads in Linux
Thread creation and activation
Linux schedulers
Time management
How implement periodic threads
How to structure RT applications
How to use a graphics library
How to simulate RT control systems
Course outline - 3
23
Teaching material
http://retis.sssup.it/~giorgio/rts-MECS.htmlCourse homepage
Books:
Third EditionPitagora, 2006Third EditionPitagora, 2006
Third EditionSpringer, 2011Third EditionSpringer, 2011
24
Final Exam
It consists of two parts:
1. Project work
2. Written test
Project: Developing a RT application under Linux, usingthe Pthread library and the Allegro graphics library.
Test: A number of questions and exercises on thecourse program.
14/10/2015
5
Embedded systems
They are computing systems hidden in an object to controlits functions, enhance its performance, manage the availableresources and simplify the interaction with the user.
Environmentactuators
sensors
micro-processor
communication
user other units
Object
Control system components
the system to be controlled– it may include sensors and actuators
the controller– it sends signals to the system according to a
predetermined control objective
the environment in which the system operates
In every control application, we can distinguish 3basic components:
A typical control system
Environ-ment
SystemController
feedback
Detailed block diagram
Other activities
filtering, classification, data fusion, recognition, planning
Environ.
System
Controller
Sensoryprocessing
internal state
external statepre-processing
feedback
actuators
sensor sensor
Software vision
INPUT
OUTPUT
task buffer
14/10/2015
5
Embedded systems
They are computing systems hidden in an object to controlits functions, enhance its performance, manage the availableresources and simplify the interaction with the user.
Environmentactuators
sensors
micro-processor
communication
user other units
Object
Control system components
the system to be controlled– it may include sensors and actuators
the controller– it sends signals to the system according to a
predetermined control objective
the environment in which the system operates
In every control application, we can distinguish 3basic components:
A typical control system
Environ-ment
SystemController
feedback
Detailed block diagram
Other activities
filtering, classification, data fusion, recognition, planning
Environ.
System
Controller
Sensoryprocessing
internal state
external statepre-processing
feedback
actuators
sensor sensor
Software vision
INPUT
OUTPUT
task buffer
14/10/2015
5
Embedded systems
They are computing systems hidden in an object to controlits functions, enhance its performance, manage the availableresources and simplify the interaction with the user.
Environmentactuators
sensors
micro-processor
communication
user other units
Object
Control system components
the system to be controlled– it may include sensors and actuators
the controller– it sends signals to the system according to a
predetermined control objective
the environment in which the system operates
In every control application, we can distinguish 3basic components:
A typical control system
Environ-ment
SystemController
feedback
Detailed block diagram
Other activities
filtering, classification, data fusion, recognition, planning
Environ.
System
Controller
Sensoryprocessing
internal state
external statepre-processing
feedback
actuators
sensor sensor
Software vision
INPUT
OUTPUT
task buffer
14/10/2015
5
Embedded systems
They are computing systems hidden in an object to controlits functions, enhance its performance, manage the availableresources and simplify the interaction with the user.
Environmentactuators
sensors
micro-processor
communication
user other units
Object
Control system components
the system to be controlled– it may include sensors and actuators
the controller– it sends signals to the system according to a
predetermined control objective
the environment in which the system operates
In every control application, we can distinguish 3basic components:
A typical control system
Environ-ment
SystemController
feedback
Detailed block diagram
Other activities
filtering, classification, data fusion, recognition, planning
Environ.
System
Controller
Sensoryprocessing
internal state
external statepre-processing
feedback
actuators
sensor sensor
Software vision
INPUT
OUTPUT
task buffer
14/10/2015
5
Embedded systems
They are computing systems hidden in an object to controlits functions, enhance its performance, manage the availableresources and simplify the interaction with the user.
Environmentactuators
sensors
micro-processor
communication
user other units
Object
Control system components
the system to be controlled– it may include sensors and actuators
the controller– it sends signals to the system according to a
predetermined control objective
the environment in which the system operates
In every control application, we can distinguish 3basic components:
A typical control system
Environ-ment
SystemController
feedback
Detailed block diagram
Other activities
filtering, classification, data fusion, recognition, planning
Environ.
System
Controller
Sensoryprocessing
internal state
external statepre-processing
feedback
actuators
sensor sensor
Software vision
INPUT
OUTPUT
task buffer
14/10/2015
5
Embedded systems
They are computing systems hidden in an object to controlits functions, enhance its performance, manage the availableresources and simplify the interaction with the user.
Environmentactuators
sensors
micro-processor
communication
user other units
Object
Control system components
the system to be controlled– it may include sensors and actuators
the controller– it sends signals to the system according to a
predetermined control objective
the environment in which the system operates
In every control application, we can distinguish 3basic components:
A typical control system
Environ-ment
SystemController
feedback
Detailed block diagram
Other activities
filtering, classification, data fusion, recognition, planning
Environ.
System
Controller
Sensoryprocessing
internal state
external statepre-processing
feedback
actuators
sensor sensor
Software vision
INPUT
OUTPUT
task buffer
14/10/2015
6
Types of control systems
Monitoring Systems– do not modify the environment
Open-loop control systems– loosely modify the environment
Closed-loop control systems– tight interaction between perception and action
Depending of the system-environment interactions,we can distinguish 3 types of control systems:
Do not have actuators Do not modify the environment
Monitoring Systems
Examples: Environmental monitoring, surveillance systems,air traffic control
Environ-ment
Dataprocessing
sensors
sensors
sensors...
Real-time system
Display
Modify the environment, actions are mostly pre-programmed,so loosely coupled with the current state of the environment:
Loosely-coupled control systems
SystemController actuators
sensorsData
processingPlanning
Environment
Examples: painting robots, assembly robots, sorting robots
Environment
SystemController actuators
sensorsData
processingPlanning
Sensing and control are tightly coupled and occur atdifferent hierarchical level:
Tightly-coupled control systems
Examples: flight control systems, military systems,advanced robots, living beings
Hierarchical control
Environment
S1
S2
S3
A1
A2
A3
F1
F2
F3
Sensing Control
high-levelcommand
high-levelrecognition
low-levelactuation
low-levelacquisition
Implications
The tight interaction with the environmentrequires the system to react to events withinprecise timing constraints.
Timing constraints are imposed by theperformance requirements and the dynamics ofthe system to be controlled.
The operating system must be able toexecute tasks within timing constraints.
14/10/2015
6
Types of control systems
Monitoring Systems– do not modify the environment
Open-loop control systems– loosely modify the environment
Closed-loop control systems– tight interaction between perception and action
Depending of the system-environment interactions,we can distinguish 3 types of control systems:
Do not have actuators Do not modify the environment
Monitoring Systems
Examples: Environmental monitoring, surveillance systems,air traffic control
Environ-ment
Dataprocessing
sensors
sensors
sensors...
Real-time system
Display
Modify the environment, actions are mostly pre-programmed,so loosely coupled with the current state of the environment:
Loosely-coupled control systems
SystemController actuators
sensorsData
processingPlanning
Environment
Examples: painting robots, assembly robots, sorting robots
Environment
SystemController actuators
sensorsData
processingPlanning
Sensing and control are tightly coupled and occur atdifferent hierarchical level:
Tightly-coupled control systems
Examples: flight control systems, military systems,advanced robots, living beings
Hierarchical control
Environment
S1
S2
S3
A1
A2
A3
F1
F2
F3
Sensing Control
high-levelcommand
high-levelrecognition
low-levelactuation
low-levelacquisition
Implications
The tight interaction with the environmentrequires the system to react to events withinprecise timing constraints.
Timing constraints are imposed by theperformance requirements and the dynamics ofthe system to be controlled.
The operating system must be able toexecute tasks within timing constraints.
14/10/2015
6
Types of control systems
Monitoring Systems– do not modify the environment
Open-loop control systems– loosely modify the environment
Closed-loop control systems– tight interaction between perception and action
Depending of the system-environment interactions,we can distinguish 3 types of control systems:
Do not have actuators Do not modify the environment
Monitoring Systems
Examples: Environmental monitoring, surveillance systems,air traffic control
Environ-ment
Dataprocessing
sensors
sensors
sensors...
Real-time system
Display
Modify the environment, actions are mostly pre-programmed,so loosely coupled with the current state of the environment:
Loosely-coupled control systems
SystemController actuators
sensorsData
processingPlanning
Environment
Examples: painting robots, assembly robots, sorting robots
Environment
SystemController actuators
sensorsData
processingPlanning
Sensing and control are tightly coupled and occur atdifferent hierarchical level:
Tightly-coupled control systems
Examples: flight control systems, military systems,advanced robots, living beings
Hierarchical control
Environment
S1
S2
S3
A1
A2
A3
F1
F2
F3
Sensing Control
high-levelcommand
high-levelrecognition
low-levelactuation
low-levelacquisition
Implications
The tight interaction with the environmentrequires the system to react to events withinprecise timing constraints.
Timing constraints are imposed by theperformance requirements and the dynamics ofthe system to be controlled.
The operating system must be able toexecute tasks within timing constraints.
14/10/2015
6
Types of control systems
Monitoring Systems– do not modify the environment
Open-loop control systems– loosely modify the environment
Closed-loop control systems– tight interaction between perception and action
Depending of the system-environment interactions,we can distinguish 3 types of control systems:
Do not have actuators Do not modify the environment
Monitoring Systems
Examples: Environmental monitoring, surveillance systems,air traffic control
Environ-ment
Dataprocessing
sensors
sensors
sensors...
Real-time system
Display
Modify the environment, actions are mostly pre-programmed,so loosely coupled with the current state of the environment:
Loosely-coupled control systems
SystemController actuators
sensorsData
processingPlanning
Environment
Examples: painting robots, assembly robots, sorting robots
Environment
SystemController actuators
sensorsData
processingPlanning
Sensing and control are tightly coupled and occur atdifferent hierarchical level:
Tightly-coupled control systems
Examples: flight control systems, military systems,advanced robots, living beings
Hierarchical control
Environment
S1
S2
S3
A1
A2
A3
F1
F2
F3
Sensing Control
high-levelcommand
high-levelrecognition
low-levelactuation
low-levelacquisition
Implications
The tight interaction with the environmentrequires the system to react to events withinprecise timing constraints.
Timing constraints are imposed by theperformance requirements and the dynamics ofthe system to be controlled.
The operating system must be able toexecute tasks within timing constraints.
14/10/2015
7
A robot control example
Consider a mobile robot equipped with:
two actuated wheels;
two proximity (US) sensors;
a mobile (pan/tilt) camera;
a wireless transceiver.
Goal Follow a path based on visual feedback; Avoid obstacles;
Send complete robot status every 20 ms.
Design requirements
Modularity : a subsystem must be developed withoutknowing the details of other subsystems (team work).
Configurability : software must be adapted to differentsituations (through the use of suitable parameters) withoutchanging the source code.
Portability : minimize code changes when porting the systemto different hardware platforms.
Predictability : allow the estimation of maximum delays.
Efficiency : optimize the use of available resources(computation time, memory, energy).
Modularity
Modularity can be achieved by:
partitioning the system into a set of subsystems, eachmanaged by one or more computational tasks;
defining precise interfaces between tasks, each specifying:
data exchanged with the other tasks (input and output)
functionality of the task (what it has to do)
validity assumptions (e.g., admissible ranges)
performance requirements (priority, period, deadline, jitter)
Asynchronous communication mechanisms.
Control view
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
1 ms1 ms
5 ms
10 ms
20 ms
100 ms
feature
extraction
object
recognition
motorcontrol
motorcontrol
motorcontrol
motorcontrol
Software View
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
featureextraction
objectrecognition
motorcontrol
periodic task buffer
EnvironmentRT System
y
x (t)
(t+)
Real-Time System
It is a system in which the correctness dependsnot only on the output values, but also on the timeat which results are produced.
tt
REAL means that system time must be synchronizedwith the time flowing in the environment.
14/10/2015
7
A robot control example
Consider a mobile robot equipped with:
two actuated wheels;
two proximity (US) sensors;
a mobile (pan/tilt) camera;
a wireless transceiver.
Goal Follow a path based on visual feedback; Avoid obstacles;
Send complete robot status every 20 ms.
Design requirements
Modularity : a subsystem must be developed withoutknowing the details of other subsystems (team work).
Configurability : software must be adapted to differentsituations (through the use of suitable parameters) withoutchanging the source code.
Portability : minimize code changes when porting the systemto different hardware platforms.
Predictability : allow the estimation of maximum delays.
Efficiency : optimize the use of available resources(computation time, memory, energy).
Modularity
Modularity can be achieved by:
partitioning the system into a set of subsystems, eachmanaged by one or more computational tasks;
defining precise interfaces between tasks, each specifying:
data exchanged with the other tasks (input and output)
functionality of the task (what it has to do)
validity assumptions (e.g., admissible ranges)
performance requirements (priority, period, deadline, jitter)
Asynchronous communication mechanisms.
Control view
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
1 ms1 ms
5 ms
10 ms
20 ms
100 ms
feature
extraction
object
recognition
motorcontrol
motorcontrol
motorcontrol
motorcontrol
Software View
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
featureextraction
objectrecognition
motorcontrol
periodic task buffer
EnvironmentRT System
y
x (t)
(t+)
Real-Time System
It is a system in which the correctness dependsnot only on the output values, but also on the timeat which results are produced.
tt
REAL means that system time must be synchronizedwith the time flowing in the environment.
14/10/2015
7
A robot control example
Consider a mobile robot equipped with:
two actuated wheels;
two proximity (US) sensors;
a mobile (pan/tilt) camera;
a wireless transceiver.
Goal Follow a path based on visual feedback; Avoid obstacles;
Send complete robot status every 20 ms.
Design requirements
Modularity : a subsystem must be developed withoutknowing the details of other subsystems (team work).
Configurability : software must be adapted to differentsituations (through the use of suitable parameters) withoutchanging the source code.
Portability : minimize code changes when porting the systemto different hardware platforms.
Predictability : allow the estimation of maximum delays.
Efficiency : optimize the use of available resources(computation time, memory, energy).
Modularity
Modularity can be achieved by:
partitioning the system into a set of subsystems, eachmanaged by one or more computational tasks;
defining precise interfaces between tasks, each specifying:
data exchanged with the other tasks (input and output)
functionality of the task (what it has to do)
validity assumptions (e.g., admissible ranges)
performance requirements (priority, period, deadline, jitter)
Asynchronous communication mechanisms.
Control view
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
1 ms1 ms
5 ms
10 ms
20 ms
100 ms
feature
extraction
object
recognition
motorcontrol
motorcontrol
motorcontrol
motorcontrol
Software View
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
featureextraction
objectrecognition
motorcontrol
periodic task buffer
EnvironmentRT System
y
x (t)
(t+)
Real-Time System
It is a system in which the correctness dependsnot only on the output values, but also on the timeat which results are produced.
tt
REAL means that system time must be synchronizedwith the time flowing in the environment.
14/10/2015
7
A robot control example
Consider a mobile robot equipped with:
two actuated wheels;
two proximity (US) sensors;
a mobile (pan/tilt) camera;
a wireless transceiver.
Goal Follow a path based on visual feedback; Avoid obstacles;
Send complete robot status every 20 ms.
Design requirements
Modularity : a subsystem must be developed withoutknowing the details of other subsystems (team work).
Configurability : software must be adapted to differentsituations (through the use of suitable parameters) withoutchanging the source code.
Portability : minimize code changes when porting the systemto different hardware platforms.
Predictability : allow the estimation of maximum delays.
Efficiency : optimize the use of available resources(computation time, memory, energy).
Modularity
Modularity can be achieved by:
partitioning the system into a set of subsystems, eachmanaged by one or more computational tasks;
defining precise interfaces between tasks, each specifying:
data exchanged with the other tasks (input and output)
functionality of the task (what it has to do)
validity assumptions (e.g., admissible ranges)
performance requirements (priority, period, deadline, jitter)
Asynchronous communication mechanisms.
Control view
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
1 ms1 ms
5 ms
10 ms
20 ms
100 ms
feature
extraction
object
recognition
motorcontrol
motorcontrol
motorcontrol
motorcontrol
Software View
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
featureextraction
objectrecognition
motorcontrol
periodic task buffer
EnvironmentRT System
y
x (t)
(t+)
Real-Time System
It is a system in which the correctness dependsnot only on the output values, but also on the timeat which results are produced.
tt
REAL means that system time must be synchronizedwith the time flowing in the environment.
14/10/2015
7
A robot control example
Consider a mobile robot equipped with:
two actuated wheels;
two proximity (US) sensors;
a mobile (pan/tilt) camera;
a wireless transceiver.
Goal Follow a path based on visual feedback; Avoid obstacles;
Send complete robot status every 20 ms.
Design requirements
Modularity : a subsystem must be developed withoutknowing the details of other subsystems (team work).
Configurability : software must be adapted to differentsituations (through the use of suitable parameters) withoutchanging the source code.
Portability : minimize code changes when porting the systemto different hardware platforms.
Predictability : allow the estimation of maximum delays.
Efficiency : optimize the use of available resources(computation time, memory, energy).
Modularity
Modularity can be achieved by:
partitioning the system into a set of subsystems, eachmanaged by one or more computational tasks;
defining precise interfaces between tasks, each specifying:
data exchanged with the other tasks (input and output)
functionality of the task (what it has to do)
validity assumptions (e.g., admissible ranges)
performance requirements (priority, period, deadline, jitter)
Asynchronous communication mechanisms.
Control view
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
1 ms1 ms
5 ms
10 ms
20 ms
100 ms
feature
extraction
object
recognition
motorcontrol
motorcontrol
motorcontrol
motorcontrol
Software View
mot_dx mot_sxpan tiltcamera US2US1
visualtracking
obstacleavoidance
vehiclecontrol
visual‐basednavigation
featureextraction
objectrecognition
motorcontrol
periodic task buffer
EnvironmentRT System
y
x (t)
(t+)
Real-Time System
It is a system in which the correctness dependsnot only on the output values, but also on the timeat which results are produced.
tt
REAL means that system time must be synchronizedwith the time flowing in the environment.
14/10/2015
8
RTOS responsibilities
A real-time operating system is responsible for:
Managing concurrency;
Activating periodic tasks at the beginning of eachperiod (time management);
Deciding the execution order of tasks (scheduling);
Solving possible timing conflicts during the accessof shared resources (mutual exclusion);
Manage the timely execution of asynchronousevents (interrupt handling).
Typical objection
AnswerGiven an arbitrary computer speed, we mustalways guarantee that timing constraints can bemet. Testing is NOT sufficient.
It is not worth to invest in RT theory, becausecomputer speed is increasing exponentially, andall timing constraints can eventually be handled.
Real-Time Fast
A real-time system is not a fast system.
Speed is always relative to a specificenvironment.
Running faster is good, but does notguarantee a correct behavior.
Speed vs. Predictability
The objective of a real-time system is to guaranteethe timing behavior of each individual task.
The objective of a fast system is to minimize theaverage response time of a task set. But …
Don’t trust the average when you have toguarantee individual performance
Sources of non determinism
Architecture cache, pipelining, interrupts, DMA
Operating system scheduling, synchronization, communication
Language lack of explicit support for time
Design methodologies lack of analysis and verification techniques
Traditional (wrong) approach
In spite of this large application domain, most ofRT applications are designed using empiricaltechniques:
– assembly programming
– timing through dedicated timers
– control through driver programming
– priority manipulation
14/10/2015
9
Disadvantages
1. Tedious programming which heavilydepends on programmer’s ability
2. Difficult code understanding
Readability 1
efficiency
Disadvantages
3. Difficult software maintainability
Complex appl.s consists of millions lines of code
Code understanding takes more that re-writing
But re-writing is VERY expensive and bug prone
4. Difficult to verify timing constraints withoutexplicit support from the OS and the language
Implications
Such a way of programming RT applicationsis very dangerous.
It may work in most situations, but the risk ofa failure is high.
When the system fails is very difficult tounderstand why.
low reliability
Accidents due to SW
Task overrun during LEM lunar landing
First flight of the Space Shuttle (synch)
Ariane 5 (overflow)
Airbus 320 (cart task)
Airbus 320 (holding task)
Pathfinder (reset for timeout)
Lessons learned
Tests, although necessary, allow only apartial verification of system’s behavior.
Predictability must be improved at the level ofthe operating system.
The system must be designed to be fault-tolerantand handle overload conditions.
Critical systems must be designed underpessimistic assumptions.
Murphy’s Laws
If something can go wrong, it will go wrong
If a system stops working, it will do itat the worst possible time
Sooner or later, the worst possiblecombination of circumstances will occur